Interpretive Summary: INTERPRETATIVE SUMMARY This study compares the efficacy of two bee species, Osmia cornuta and Apis ifera as pollinators of 'Delicious' apple flowers. Osmia cornuta always col both pollen and nectar on the same flower and pollinate all the flowers the eit. Most Apis mellifera collect only nectar and pollinate a third of the f they visit. Flowers visited by Osmia cornuta are five times more likely to fruit than those visited by Apis mellifera nectar collectors. Apis mellifer len collectors were very scarce, but pollinated almost all the flowers they ted. During the flowering period of the study orchard, an individual Osmia ta visited an average of 22,252 apple flowers. From these results it is est d that 530 nesting Osmia cornuta are enough to pollinate one ha of apple tr

Technical Abstract:
TECHNICAL ABSTRACT The foraging behavior and pollinating efficacy of Osmia cornuta and Apis me ra were studied in a 'Delicious' apple orchard in NE Spain. Yields after on gle visit were more than five times higher in flowers visited by O. cornuta a in those visited by A. mellifera nectar gatherers. This result is attribu the lower rate of stigma contact in A. mellifera visits, rather than to in cient deposition of compatible pollen when the stigmata are contacted. A. m era pollen collectors had very high rates of stigma contact, but they were scarce (3%) on 'Delicious' flowers, despite the presence of abundant brood eir hives. One single visit per flower by O. cornuta produced commercial fr et (27.4% fruits/flower) and fruit size (> 70 mm diameter). Based on cell p tion, average number of trips required to provision a male and a female cel ld flower visiting rates, it is estimated that a mean of 22,252 apple flowe ts per female O. cornuta were made during the 15-day flowering period. This lt indicates that 530 nesting O. cornuta females per ha are enough to provi equate pollination.